I just finished reading "The Idiot's Guide to Music Theory" and am a little confused about minor scales. This book presented three different minor scales...natural, harmonic, and melodic. I don't really understand the need for three different minor scales when there is only one major and one of each mode...can someone help me out with this?
Take em as 3 entirely different scales without trying to relate em, lol. All 3 are from 3 different modes. But as far as the way they are named, both harmonic and melodic share the minor 3rd, is why i guess they're called minors.
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melodic and harmonic minor are alterations to the natural minor scale. For now I'd focus on learning the Major scale, and how the natural minor relates to it. Pretty much any other scale/mode you'll need to use can be derived from the major scale, so get that nailed and you've done all the hard work

If you look at the scales in terms of intervals

Major = R 2 3 4 5 6 7
natural minor = R 2 b3 4 5 b6 b7

The b3 determines that its a minor scale

Harmonic minor is the natural minor with a raised 7th
harm min = R 2 b3 4 5 b6 7

Melodic minor is the natural minor with a raised 6th and 7th
melodic min = R 2 b3 4 5 6 7

Harmonic and melodic minor are not modes of the major scale - but they do have their own modes.
The minor scale has a minor third minor sixth and minor seventh.

If we build a chord from the fifth degree of the scale it is minor in quality (because the minor seventh in the scale becomes the minor third of the chord)
For example think of the key of Am.
The natural minor scale is A B C D E F G A
If we build a chord from the fifth -the E we get E G B. That makes an Em.

Composers throughout the ages found that even when in a minor scale the chord built using the fifth scale degree as a root always resolved better when it was major in quality and used the "leading tone" or major seventh degree. In Am scale that would be E major (E G♯ B). You can hear this in Am by playing Am - Em - Am and then by listening to the difference when you play Am - E major - Am. If you notice in Am to get that E major we have to raise the G to a G♯.

So we would be playing with A natural minor (A B C D E F G) but then when we want a strong harmonic resolution we use E major which means a slight alteration to the scale for that chord. The scale would then be A B C D E F G♯.

It became so common place to make this alteration that it came to be known by it's own name - the harmonic minor scale. So called because it's sole purpose was to increase the harmonic resolution in a V-i harmonic progression.

Those composers also found that when they were playing melodically and ascending toward the root through the scale the half step from the major seventh to the tonic (say from G♯ to A) almost always had a much more pleasing sound than when they used the minor seventh which is a whole step below the tonic. E F G A - try to target the A so you hit it right on an Am chord change. It sounds all right but the G♯-A move sounds much stronger.

They couldn't just use the major seventh though because the run became a little all over the place. The perfect fifth to the minor sixth (a half step) then up to the major seventh (three half steps) followed by the tonic (half step) was a disjointed and not very smooth melodic run. E F G♯ A - If you play it you should hear it as a little bit of a bumpy ride considering we are just moving up the scale step by step.

The problem they faced was that when ascending they wanted the semitone move from the major seventh to the tonic, but not the three-semitone leap from the minor sixth to the major seventh.

The solution was to use a major sixth as well. So you end up with a perfect fifth a major sixth and a major seventh when ascending toward the root melodically. Since this alteration was used for melodic purposes it was called the melodic minor scale. The run would end up as E F♯ G♯ A which is a lot smoother and keeps the G♯-A move they were so keen on.

When descending away from the root the half step resolution wasn't really an issue like it was when targeting the tonic from below. When descending the natural minor scale was perfectly acceptable. The melodic minor then was an alteration to the natural minor scale when ascending melodically targeting the root. And it too became such a common place alteration for that specific reason it got it's own name too - the melodic minor scale.

As you can see - like zhilla said - they are all related to the natural minor scale. MonsterOfRock doesn't quite know what he's talking about on this one. They are related to the natural minor scale, they were traditionally not used as three distinct scales but as specific alterations for specific purposes of the same minor scale, and they are not from different modes. He is right in that they are called minor (partly) because of their minor third. They are called minor because the base triad formed from the tonic are minor chords - that is they have a root, minor third and perfect fifth.
Last edited by 20Tigers at Sep 30, 2009,
^Kudos 20Tigers. That was a great explanation. Just hope the OP can understand it...

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Quote by MonsterOfRock
Take em as 3 entirely different scales without trying to relate em, lol. All 3 are from 3 different modes. But as far as the way they are named, both harmonic and melodic share the minor 3rd, is why i guess they're called minors.

That's just it, they aren't three entirely different scales at all, the harmonic minor and melodic minor are simply alterations of the natural minor scale introduced by composers to make for easier resolutions - it's got nothing to do with modes.
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Just hope the OP can understand it...
that was my only worry too. I didn't take the time to explain deeply enough so that it answered any questions it raised. If he doesn't get it or some of the things in it I hope he feels confident enough to ask more questions.